This program is composed of several projects, each of which deals with an aspect of pernatal respiration. Project A centers on studying the effects of exercise upon gas transport during pregnancy. Project B is concerned with an investigation of the effects of uterine ischemia during pregnancy in dogs and the biochemical characteristics of canine uterine renin (as compared with canine renal renin). Project C deals with the mechanisms of solute transfer between maternal and fetal blood in guinea pigs and sheep. Project D is oriented toward an investigation of the effects of incubator gas concentrations upon the development of the avian embryo. Project E centers around measurements of the distribution of fetal cardiac output in sheep. In Project F we are investigating mechanisms controlling fetal water balance in chronically-prepared sheep fetuses. Project J is concerned with the effects of respiratory depression during pregnancy using female methadone addicts as subjects, and with developing an animal model for the methadone maintenance syndrome.